Add personal knowledge base workflow

[unityequilibrium]

Summary

• Add a local personal knowledge-base helper for status, changed-file ingest, and search
• Document the personal-first knowledge-system architecture and ingestion plan
• Ignore generated local KB SQLite files

Verification

• py_compile docs/knowledge_base/personal_kb.py
• python -m docs.knowledge_base.personal_kb status
• git diff --check origin/main..HEAD